My trusty 2GM20F has been running flawlessly for many years. Sooner or later I was bound to run into something I was going to have to deal with.

For the last 50 or so hours of operation I have noted an excessive amount of WHITE smoke along with a very obvious fueley smell.

Given the boat completed a sail to Hawaii and back last year, a trip which included a lot of at sea refueling from 5 gal jugs, I figured first step would be to completely clean tank, filters and lines up to the hi pressure fuel pump. Accomplished this and also upgraded the primary filter to a compact Racor fuel water separating filter assembly with a bowl. Previous filter was just a filter, no observation bowl. Also purchased a diesel dry additive to enhance water protection and to clean injectors to the extent an additive can actually clean them. I did find some debris in the tank and some slight gelling plus quite a bit of dirt and a little water. It was not a shocking amount of contaminate. I have now run about 20 gals of known clean and treated diesel through the system and white smoke is still an issue.

Oil burn seems minimal minimal - about 8 ounces per 40 hrs running (engine hours at about 1800 - best estimate including WAG on POs usage)No coolant is being consumedEngine power is nominal at all RPMengine runs well, no weird noisesAir cleaner has been replaced and is cleanI did note hard starting in colder weather (40s 50s) but this symptom seems to have cleared with warmer weather (60s) and possibly clean/treated fuel benefit. Engine historically started up quickly in all weather here in California.

The plan going forward is:

1. perform compression test - tools on the way - if this fails I need to reboot my strategy, I am banking on compression being OK due to overall engine performance being OK2. Remove and replace both injectors - injectors on the way (never been replaced during my ownership - 1200 hours)3. perform valve clearance inspection and adjustment - never been done (yea, I know)

The causes Geoff mentions give a white/ light grey smoke which also stinks.Another cause and giving white smoke which doesn't stink: too little water injection in the exhaust systemresulting in a too high exhaust temperature giving water vapour.

I believe I am good on water flow through the mixing elbow/exhaust. I replaced the elbow several years ago due to zero water flow so been there done that. Today I have excellent flow through the system as evidenced by good water flow at the exhaust, no overheating indications including smells of burning rubber and the like.

I am really hoping it is the injectors which seem the most likely suspect. Compression issues sound like money unless it is something simple like poorly adjusted valve clearances. Fuel injection timing might also be fixable on a DYI basis but the procedures to time the fuel injection look tricky.

As a general note, it is too bad there is not a comprehensive fault tree on these engines. I have to believe that there are other indicators of, say injector issues vs compression issues but nothing I have seen takes you to the next level. You read white smoke could be caused by these six things. Fuel smelling white smoke with no oil burn and no coolant burn reduces the possibilities but then the fault tree seems to come full stop. Seems like there could be some further indications which would lead you to suspect injectors vs compression but I've not been able to find these discussed anywhere.

replaced the injectors with rebuilt units and she fires up and runs just like she used to. No white smoke, all is good.

Bottom line was an injector issue. I bought three rebuilt injectors, replaced both in the engine so I have one left. I will hove one of the two originals rebuilt in order to have a complete set of spares on the boat. Learned a lot doing this project myself, very worthwhile.

I never did a compression test. I was saving that for last ditch effort if injectors did not work.

I bought a torque wrench for this project (about $35 on Amazon) this was really useful. When I pulled the injectors I felt like the hold down flanges were not very tight. Now I am sure they are torqued to factory spec.

raggededge wrote:I have a 1988 Freedom 28 with a Yanmar 2GM20F.....every time I use the boat under power the transom develops a black mustache......easy to remove with soap and water, but why does it happen?

Thanks,

Jeff Palmer

Jeff,

I'm sure others will comment but in my experience, some diesel soot on the transom is inevitable, even for a properly running engine. How much soot is a subjective call but in my case it's sort of like a dirty windshield look. Not dense black but a variegated dirtiness which is most visible within 18 inches either side of the exhaust out and extending up the transom about a foot. Short motor (1 hr) No issue, long motoring ( 12 hrs) definite visible build up (think dirty windshield only black not brown). If it's a lot worse, you may have something going on. Are you seeing any visible engine smoke? If so, what color?

I have seen a few boats which have a small flexible hose attached to the exhaust outlet. This places the actual exhaust output about 18 inches behind the boat when motoring. I assume the intention is to keep the soot off the transom and gases out of one's lungs. Such an extension would probably not be desirable on our boats where the exhaust outlet is very near the waterline.